Hospital integrates lighting, HVAC to accomplish goals
Dell Children’s Medical Center of Central Texas recently completed integrating a BAS with a lighting control system using a BACnet interface between the two systems.
Dell Children’s Medical Center of Central Texas (DCMCCT) recently completed construction on a 76,000-sq-ft, 72-bed, 3-story expansion. The design for DCMCCT integrated a BAS with a lighting control system using a BACnet interface between the two systems. The systems integrated included a Siemens BAS and an Acuity nLight control system. While the building was awarded U.S. Green Building Council LEED Platinum and many factors made this possible, the lighting and HVAC controls played a large role in accomplishing this goal.
The project was originally designed to use many different lighting schemes, and the lighting system was designed so that the program can be easily adjusted as use of spaces become more defined after the system has been in operation over time. Original programming included spaces that have set time-of-day occupancy, such as visitor spaces, waiting rooms, conference rooms, and work rooms. These are controlled via occupancy sensor with different durations for automatic shutoff during the day than at night, allowing for shorter shutoff times to turn off lights when in the unoccupied mode at night. All corridor lighting is reduced by 70% to 30% output from 10 p.m. to 6 a.m. Nurse stations dim by 50% from 10 p.m. to 6 a.m. Other support spaces use timer switches. Spaces located adjacent to windows also use photocells to adjust lighting output to meet predetermined light levels for each space.
The programming interface is flexible enough to allow post-occupancy changes. One example of a change that has been made since owner occupancy is the strategy used in the corridors. Originally, the system was programmed to use occupancy sensors in the corridors to turn lights up in the evening when activated by motion. After a short time in operation, the staff stated a preference for the lights to simply stay at the 30% output.
Patient rooms have a variety of control sequences depending on occupancy. Each patient room is equipped with a low-voltage manual switch that allows for the rooms to be put in occupied or unoccupied mode. The system also includes the ability for future integration of the occupied or unoccupied mode automatically with the hospital’s billing software system. This integration will allow a room to be placed into the correct mode based on a bed’s occupied status. The room’s controls then act differently depending on the occupied mode. These parameters allow both the lighting and HVAC systems to operate more efficiently. As an example of unoccupied mode control, when a patient room is in unoccupied mode and the housekeeping staff enters the room for cleaning, all lighting within the space will operate using occupancy sensors.
The HVAC system terminal boxes are also controlled through the occupied/unoccupied mode status. In the unoccupied mode, the terminal box minimum airflow cubic feet/minute (cfm) setpoints are reduced. Unoccupied rooms allow for lower minimum cfm setpoints due to lower outside air and code-mandated air change requirements.
The lighting control system is also integrated into other typical hospital systems, including the nurse call “code blue” system. When a patient room’s code blue button is activated, all lighting within the room and the corridors is turned on to maximum brightness to aid in the emergency response. Similarly, there is an epilepsy-monitoring unit on a floor for diagnosing people with seizures. The lighting control system is integrated in those spaces similarly to the code blue scenario. Upon an alarm from the specialized epilepsy equipment, all lights within the room are turned on to maximum brightness, similar to a code blue. This helps staff address the issue and gives them one less item to worry about during a seizure event.
The system at DCMCCT also includes control of plug loads, including automatically turning off televisions in public spaces after visitors’ hours are over and providing minimum airflows for the HVAC system in public spaces that were unoccupied.
Preliminary energy usage numbers indicate that the building is performing almost 16% better than anticipated by the energy model, which already indicates the building is performing 18% better than the ASHRAE 90.1-2007 baseline hospital. While it is difficult to put an exact figure on how much the occupancy integration of all these systems is worth the overall reduction of energy, user satisfaction indicates that the design meets the client’s goals.
Douglas Lacy is a senior associate and project manager with ccrd partners. He serves as a lead electrical engineer, is group production coordinator, and manages variety of projects including hospitals, corporate headquarters, and data centers. Shaun Grimm is an associate principal and project manager with ccrd partners. He is the lead electrical engineer, and leads the electrical design of different projects including hospitals, institutional facilities, and office buildings.